An experimenter puts 5 monkeys in a large cage. High up at the top of the cage, well beyond the reach of the monkeys, is a bunch of bananas. Underneath the bananas is a ladder.

The monkeys immediately spot the bananas and one begins to climb the ladder. As he does, however, the experimenter sprays him with a stream of cold water. Then, he proceeds to spray each of the other monkeys.

The monkey on the ladder scrambles off. And all 5 sit for a time on the floor, wet, cold, and bewildered. Soon, though, the temptation of the bananas is too great, and another monkey begins to climb the ladder. Again, the experimenter sprays the ambitious monkey with cold water and all the other monkeys as well. When a third monkey tries to climb the ladder, the other monkeys, wanting to avoid the cold spray, pull him off the ladder and beat him.

Now one monkey is removed and a new monkey is introduced to the cage. Spotting the bananas, he naively begins to climb the ladder. The other monkeys pull him off and beat him.

Here’s where it gets interesting. The experimenter removes a second one of the original monkeys from the cage and replaces him with a new monkey. Again, the new monkey begins to climb the ladder and, again, the other monkeys pull him off and beat him - including the monkey who had never been sprayed.